The present invention relates generally to plasma reaction chambers, and more particularly, to methods, systems and apparatus for plasma reaction chambers separate from the wafer processing chamber.
FIG. 1A is a side view of a typical parallel-plate, capacitive, plasma processing chamber 100. FIG. 1B is a top view of a substrate 102 processed in the typical parallel-plate, capacitive, plasma processing chamber 100. The typical plasma processes processing chamber 100 includes a top electrode 104, a substrate support 106 for supporting a substrate to be processed 102. The substrate support 106 can also be a bottom electrode. The top electrode 104 is typically a showerhead type electrode with multiple inlet ports 109. The multiple inlet ports 109 allow process gases 110 in across the width of the processing chamber 100.
The typical parallel-plate, capacitive plasma reactor 100 is used for processing round planar substrates. Common processes are dielectric etch and other etch processes. Such plasma reactors typically suffer from inherent center-to-edge non-uniformities of neutral species.
Although these systems work well, some produce center-to-edge non-uniformities of neutral species which arise from the differences in one or more of a flow velocity, an effective gas residence time, and one or more gas chemistries present at the center of the substrate as compared to the flow velocity, effective gas residence time, and one or more gas chemistries present at the edge. The one or more gas chemistries can be caused by gas-phase dissociation, exchange and recombination reactions.
By way of example, as the process gases are introduced across the width of the processing chamber the plasma 112 is formed between the top electrode 104 and bottom electrode 106 and the plasma is formed. Plasma byproducts 118 are formed by the reaction of radicals and neutrals in the plasma 112 with the surface of the substrate 102. The plasma byproducts 118 are drawn off to the sides of the substrate and into pumps 108. Plasma byproducts can include one or more dissociation reactions (e.g., CF4+e−→CF3+F+e−) and/or one or more ionizations (e.g., CF4+e−→CF3++F) and/or one or more excitations (e.g., Ar→Ar++e−) and/or one or more attachments (e.g., CF4+e−→CF3+F−) and/or one or more binary reactions (e.g., CF3+H→CF2+HF).
Plasma byproducts 118 can also include etch byproducts including the etchant, F, CFx, SiF2, SiF4, Co, CO2. Etch byproducts can also dissociate in the plasma 112.
Recombination also occurs during the plasma processing. Recombination produces recombination products 120. Recombination typically occurs when the radicals and neutrals from the plasma 112 impact surfaces such as the bottom surface of the top electrode 104. The recombination products 120 are then drawn off the side of the substrate 102 into pumps 108, similar to the plasma byproducts 118. Plasma recombination products 120 can include one or more wall or surface reactions (e.g., F+CF→CF2, and/or H+H→H2, and/or O+O→O2, and/or N+N→N2). Plasma recombination products 120 can also include deposition where CFx forms a polymer on the wall or other internal surface of the chamber 100.
It should be noted that as shown in FIG. 1A, the plasma byproducts are drawn off one side of the substrate 102 and the recombination products 120 are drawn off the opposite side of the substrate 102 for clarity purposes only. In actual practice, those skilled in the art would realize that both the recombination products 120 and the plasma byproducts 118 are intermixed and drawn off both sides of the substrate 102 to pumps 108 or other means.
As the plasma processing occurs, concentrations of the recombination products 120 and the plasma byproducts 118 vary from the center to the edge of the substrate 102. As a result, the concentrations of the process gases, radicals and neutral species in the plasma 112 also correspondingly vary. Thus, the effective plasma processing, etch in this instance, varies from the center to the edge of the substrate 102. There are, however, a number of chamber configurations and structures that can be implemented to reduce or control the plasma.
With such controls, the plasma radicals and neutral species are most concentrated at the center of the substrate 102 in plasma processing regions 114A and 116A over central portion 102A of the substrate 102. Further, the concentrations of the radicals and neutral species are somewhat less concentrated in intermediate plasma processing regions one 114B and 116B over intermediate portion 102B of the substrate 102. Further still, the concentrations of the radicals and neutral species are further diluted and less concentrated in edge plasma processing regions 114C and 116C over the edge portion 102C of the substrate 102.
Thus, plasma processing occurs fastest in the center plasma processing regions 114A and 116A over the center portion 102A of substrate 102 as compared to the plasma processing that occurs slightly slower in the intermediate plasma processing regions 114B and 116B over the intermediate portion 102B of substrate 102 and even slower in the plasma processing of the edge plasma processing regions 114C and 116C over the edge portion 102C of the substrate. This results in a center-to-edge nonuniformity of the substrate 102.
This center-to-edge nonuniformity is exacerbated in small volume product plasma processing chambers that have a very large aspect ratio. For example, a very large aspect ratio is defined as when the width W of the substrate is about four or more or more times the height H of the plasma processing region. The very large aspect ratio of the plasma processing region further concentrates the plasma byproducts 118 and recombination products 120 in the plasma processing regions 114A-116C.
Although this center-to-edge non-uniformity of neutral species is not the only cause of center-to-edge process uniformity, in many dielectric etch applications it is a significant contributor. Specifically, neutral-dependent processes such as gate or bitline mask open, photoresist strip over low-k films, highly selective contact/cell and via etch may be especially sensitive to these effects. Similar problems may apply in other parallel-plate plasma reactors, besides those used for wafer dielectric etch.
In view of the foregoing, there is a need for improving the center-to-edge uniformity in plasma etch processes.